Development and Applications of X-ray Photon Correlation Spectroscopy in the Ultra-small Angle Scattering Regime
Partially coherent radiations generated by high-brilliance third generation synchrotron sources have allowed measurements of slow dynamics in various soft and hard material systems. We have recently developed an X-ray photon correlation spectroscopy (XPCS) technique in the ultra-small angle scattering regime, which fills an existing gap between the accessible Q ranges of dynamic light scattering and pinhole-based XPCS and enables studies of low-frequency equilibrium and nonequilibrium dynamics in optically opaque materials.
This technique, based on the Bonse-Hart ultra-small angle X-ray scattering instrument at the Advanced Photon Source, requires modifications to the beamline configuration and instrument operations for dynamic measurements. We will review the basic features of this technique, and will discuss in details the optimizations that we made to meet the needs of signal-to-noise limited XPCS studies. We will present the data analysis approaches that we established to quantify the dynamic time scales of measured equilibrium or nonequilibrium processes. Finally, we will use a few examples to illustrate the applications of this technique in understanding of equilibrium dynamics of soft materials and nonequilibrium behavior of both soft and hard materials.